<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <button>获取时间</button>
  <p>当前时间</p>

  <script>
    var button = document.querySelector('button')
    var p = document.querySelector('p')

    button.onclick = function() {
      p.innerText = new Date()
    }
  </script>
</body>
</html>